Introduction and objective:
A change in the body mass may be one of the health consequence of the COVID-19 pandemic, and may affect the health condition measured in many dimensions. The paper aims at assessment of the level and determinants of the body mass changes and stress level in the initial months of the COVID-19 pandemic, and the interrelation of these two factors.

Material and methods:
Data were collected in June 2020, as a cross-sectional on-line survey. The representative sample of 2,535 Poles aged 18–65 was analysed. The main outcome is the Cohen’s stress index PSS-4. Among thirteen independent variables, five were related to the change observed during the pandemic (including the body mass change and satisfaction with sexual life).

Results:
Increase of the body mass within the period of the pandemic was declared by 33.9% of the respondents, including 36.1% in urban and 30.9% in rural areas (p=0.026). The average increase of body mass was 5.11 kg. The increase of body mass was related to the existing overweight and obesity, occurrence of chronic diseases, episodes of physical and mental crisis, and decrease of interest in sexual activity. The average index of stress in the initial months of the pandemic was 6.38±2.94. Multivariate regression analysis showed eight independent predictors of stress in the whole group, seven in towns and five in rural areas. The significance of the relationship with the body mass increase was proved only among residents of rural areas.

Conclusions:
The initial months of the COVID-19 pandemic were reflected, to a different extent, among residents of urban and rural areas. Body mass change and sexual health indicators remained significant predictors of stress level, even after analyses were corrected for other covariates.